1. Field of the Invention
This invention relates to a multi-window display control system, and in particular to a multi-window display control system suitable for a system in which a multi-window display terminal is used for a terminal of a first processor and for a terminal of a second processor having a priority higher than that of the first processor.
2. Description of the Prior Art
In a computer system, messages coming from a service processor regarding employment, maintenance, and diagnosis of the system (console messages) are displayed on a terminal exclusively used for the service processor (console terminal). While the user is using the system, business messages are displayed on a terminal exclusively used for business coming from a central processing unit (CPU) used for the business.
Recently a system permitting cost reductions by eliminating console terminals or console terminal controllers effecting the display of the messages coming from the service processor, has come into widespread use. In this system, one of a plurality of terminals, or only one terminal, disposed around a small computer system is used as both the console terminal and as the terminal for displaying business messages in order to reduce the number of required terminals.
Heretofore, in the case where a terminal having a multi-window display was used as the console terminal and as the terminal for displaying business messages, commonly one of a plurality of the terminal's virtual screen buffers was fixedly assigned for storing the messages coming from the service processor. A terminal controller wrote the messages for business sent from the CPU in a specified virtual screen buffer of a specified terminal in accordance with the terminal address and the virtual screen buffer address included in the message write-in command. The terminal controller also wrote the console messages sent from the service processor in a specified screen buffer of a specified terminal in accordance with the terminal address included in the message write-in command and the virtual screen buffer address assigned fixedly for console messages. Such a system is disclosed, e.g., in Japanese Patent Unexamined Publication No. 54-152431.
Since the console messages coming from the service processor are emergent, e.g. messages notifying of errors in the system hardware, according to prior techniques a screen buffer was fixedly assigned exclusively for the console messages. Therefore, when a console message was transmitted it was immediately received and displayed on the terminal. However, this can be inconvenient for the operator of the terminal. For example, in the case where the terminal is provided with four virtual screen buffers, four kinds of screens can be displayed alternatively on the display screen by utilizing the four virtual screen buffers, unless the terminal is constructed so as to receive the console messages. If the terminal is constructed so as to receive the console messages, only three virtual screen buffers can be used and up to three kinds of screens can alternatively be displayed.
In the foregoing example, with the same hardware construction of the terminal, the number of virtual screen buffers which can be used for the display of business is reduced in comparison with the case where the terminal is used exclusively for business. In contrast, if it is intended that the number of virtual screen buffers available for business messages on a common terminal which displays both business and console messages is to be equal to the number of virtual screen buffers of the terminals used exclusively for displaying business messages, then a virtual screen buffer used exclusively for console messages should be disposed apart from those used exclusively for business in the terminal which displays both types of messages.
In the case where the common console/business terminals are intended to have the same number of virtual screen buffers for business as the terminals used exclusively for business, it is necessary to associate a virtual screen buffer for the console messages with each of the terminals which are intended for console/business display. That raises the cost of the system.
Furthermore, there is the case where a terminal having one virtual screen buffer is used as a common console/business terminal. When console messages are frequently outputted the problem arises that the display of emergent console messages prevents the use of the terminal as a terminal for business.
The above described problem arises not only in the case where a common terminal is used for the display of console messages and for the display of business. The above described problems also arise in general in the case where a common terminal is used for the display of outputs of a plurality of processors having different output priorities.